Conventional oligonucleotide synthesis entails first binding the protected 3' terminal nucleotide to a solid support by a succinate ester linkage. The oligonucleotide is extended from the 3' end by the addition of an appropriate sequence of additional protected bases. This process yields an oligonucleotide bound to the support at its 3' end and which has a 5' functional group such as an amine or a thiol group. The oligonucleotide is then deprotected, which results in cleavage from the support, and then purified. The purified oligonucleotide is then immobilized at the 5' end to a second solid support.
Thus, the result of conventional solid phase DNA synthesis is an oligomer immobilized at the 5' end.